224 Mr. G. A. Hemsalech on the Line Spectrum of 



continue as strong lines in the latter and only slowly and 

 gradually weaken as they approach the upper part of the 

 flame (examples : W 3860, 3886, 3920). As I have already 

 pointed out in my first paper, the apparent enhancement of 

 these lines in the cone is probably caused by the super- 

 position of two independent emissions, one due to thermal 

 excitation in the outer stratum of flame and the other to 

 chemical actions in the explosion region. 



b. Oxy-coal Gas Flame. (Plate II. No. 2.) 



With the gases adjusted so as to give the highest tempera- 

 ture obtainable with this flame, the cone gives out the bands 

 of the Swan spectrum with much greater intensity than the 

 air-coal gas cone, and, in addition, many other carbon bands, 

 which are absent or appear only as traces in the latter, be- 

 come quite prominent. Class 1. lines of iron, even the most 

 intense, first become visible a little distance up from the base 

 of the cone ; they gradually increase in intensity and reach 

 a maximum in the mantle just above the cone. There is no 

 indication whatsoever that these lines are in anyway affected 

 by chemical actions in the explosion region, such »s they are 

 in the Bunsen cone. After having obtained their greatest 

 strength they die out again very gradually as the temperature 

 decreases on approaching the summit of the flame. In fact, 

 their intensities seem to be a function of the temperature. 



Class II. lines, as shown by the triplet at 4046, behave in 

 a very similar manner as Class I. lines, with this exception, 

 however, that near the base of the cone they show a very 

 slight enhancement. Of Class III. lines, only traces of a 

 very few are. seen near the base of the cone, where they 

 appear as " short " lines, reaching only a little distance up 

 from the base. An explanation for the appearance near the 

 base of the cone of these lines will be given later. 



It is thus clear that the substitution of oxygen for air sup- 

 presses those chemical actions to which the radiations of 

 Classes II. and III. are particularly sensitive, and it there- 

 fore appears that the presence of air or nitrogen in the gas- 

 mixture is essential for the emission of the cone lines. These 

 results farther show that there is no connexion between the 

 emission of the carbon bands and that of the particular types 

 of iron lines under consideration. 



c. Air-hydrogen and Oxy-hydrogen Flames. 

 (Plate III. Nos. 1 and 2.) 



Although there is a well-defined cone in the air-hydrogen 

 flame, it does not appear that it has any other than thermal 



